UVP is a much shorter time than UOCVP. UVP will trip in the seconds range, while UOCVP trips when the calculated open circuit voltage gets below the limit. For example, if you have 2.8V UVP, and 3.2V UOCVP, the battery will protect with heavy load under 2.8V, but OCV may still be above 3.3 at this time, so it will not trip UOCVP. If a very light load is applied, the cell will be much more empty at 2.8V light load than 2.8V heavy load, so a higher threshold can be used to protect the cell early and stop the discharge. In this case, a C/50 load can protect at ~50-100 mV below the UOCVP threshold.